Why are there not better anti-aircraft weapons?  On Port Valdez, rush mode, the apache is unstoppable if the right pilot is in it.  You will never lock on and never hit them enough with the few machine guns scattered around.  They need to balance this.  Better lock-on rockets or something.

I heard a little while back they were going to give AA guns a boost, and add an AA APC for the US side. I havn't played in a while though, so I don't know if that's been implemented yet.

I found that a problem as of late. And the last area on Isla Inocentes also has an unstoppable helicopter. The UAV can be used but it isn't as efficient as an anti-air gun.

" I found that a problem as of late. And the last area on Isla Inocentes also has an unstoppable helicopter. The UAV can be used but it isn't as efficient as an anti-air gun. "

The Hind specifically is actually pretty easy to deal with, if you know what to do. My strat is to take an M95 with a red dot and start picking away at it. Then, because the defenders base is at the bottom of a hill, it's easy to rocket or mortar the Hind when it lands to repair.
 
Actually, the M95 is pretty much the answer to any helicopter that nobody can seem to kill. No, you probably won't shoot them all the way down, but you can at least force them away.

The next patch (assuming you're not talking PC, which already has it) is making the "Tracer" shoot much faster. So it can actually hit a flying copter. That should be nice.

This needs fixing. I've been spawn camped quite a lot by 'copters, and there is almost no real way to stop them.

good job getting the quest

The patch (which apparently is awaiting MS/Sony certification) will increase the damage of AA guns on the heli, increase the tracer dart speed, and reduce the damage of the heli's gunner. 
 
Should be much better after that.

After the patch people playing the PC version mostly use black hawks to get to the base and jump out/crash heli.
It is now rare to see black hawks use mini guns simply because they get shot down so fast.
Tracer darts are insane fast now, and it's incredibly easy to hit helicopters with them.
And after a heli is trace'd you have to be super fast with the lock on otherwise some1 else will shoot it down before you :P
 
So yea, wait for the patch if you're playing on console. 
On PC helicopters are kinda gimped after it.

Tracers are insanely effective now since the last patch. If I play engi I can single-handedly make sure that choppers never become a problem for my team. 
 
Some intelligent pilots like to use the smoke launcher upgrade though, which really sucks for me :'(

Interesting strategies, thanks everyone!